1. Field of the Invention
The present invention relates to an actuator for use with a disk drive. More particularly, the present invention relates to an actuator for use with a disk drive having a coil assembly designed to aid in heat convection from the coil of the coil assembly.
2. Description of the Prior Art and Related Information
A huge market exists for hard disk drives for mass-market host computer systems such as servers, desktop computers, and laptop computers. To be competitive in this market, a hard disk drive should be relatively inexpensive, and should accordingly embody a design that is adapted for low-cost mass production. Further, there exists substantial competitive pressure to continually develop hard disk drives that have increasingly higher storage capacity, that provide for faster access to data, and at the same time conform to decreasingly smaller exterior sizes and shapes often referred to as “form factors.”
Satisfying these competing constraints of low-cost, small size, high capacity, and rapid access requires innovation in each of numerous components and methods of assembly including methods of assembly of various components into certain subassemblies. Typically, the main assemblies of a hard disk drive are a head disk assembly and a printed circuit board assembly.
The head disk assembly includes an enclosure including a base and a cover, at least one disk having at least one recording surface, a spindle motor for causing each disk to rotate, and an actuator arrangement. The printed circuit board assembly includes circuitry for processing signals and controlling operations. Actuator arrangements can be characterized as either linear or rotary; substantially every contemporary cost-competitive small form factor drive employs a rotary actuator arrangement.
The rotary actuator arrangement is a collection of elements of the head disk assembly; the collection typically includes certain prefabricated subassemblies and certain components that are incorporated into the head disk assembly. The prefabricated assemblies include a pivot bearing cartridge and, in some cases, a prefabricated head stack assembly which may include the pivot bearing cartridge. Other components of the rotary actuator arrangement are permanent magnets and an arrangement for supporting the magnets to produce a magnetic field for a voice coil motor. The prefabricated head stack assembly includes a coil forming another part of the voice coil motor. The prefabricated head stack assembly also includes an actuator body having a bore through it, and a plurality of arms projecting parallel to each other and perpendicular to the axis of the bore. The prefabricated head stack assembly also includes head gimbal assemblies that are supported by the arms. Each head gimbal assembly includes a load beam and a head supported by the load beam. The head is positioned over a track on a recording surface of the disk to write or read data to or from the track.
Typically, the body portion and the arms of the head stack assembly are made out of metal and form a unitary structure known as an “E-block.” The E-block may include any number of arms, e.g., one, two, three, four, five, six, etc. However, these types of head stack assemblies tend to have a relatively high mass since the entire unitary structure of the E-block is typically made out of metal. This relatively high mass results in a corresponding high moment of inertia about the pivot axis of the head stack assembly. Because of this high moment of inertia, in order to pivot the head of the head stack assembly to access data from the disk, a relatively large access time is required for the given amount of power applied to the coil.
Because of the competitive pressure to continually develop hard disk drives that provide for faster access to data, techniques are continuously being developed to decrease the access time to data. One potential technique to accomplish this is by increasing the speed at which the head stack assembly is pivoted to position the head over a track of the disk in order to access data. Unfortunately, the faster that the head stack assembly is to be moved to position the head, increased power is likewise required to be applied to the coil of the coil assembly in order to move the head of the head stack assembly at the faster rate, which further results in ever increasing temperatures of the body portion and the arms of the head stack assembly. If the temperatures of the body portion and the arms of the head stack assembly increase too much, the internal components of the hard disk drive (including the head stack assembly itself may be damaged. Furthermore, the increased temperatures may cause the resonant frequencies of the actuator to change such that the overall performance of the disk drive is degraded.